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If this is a question of accepted style then my first stop would be whoever would be likely to receive or review or grade or publish said work. Some bodies have very clear cut ideas about how things should be presented.
However if the focus here is readers then one need only consider their own expectations, memory skills, etc and the importance of the ...

Many publishers omit the information altogether when they post standalone short stories to KDP. The figure that Amazon's Product Details will give an estimate of the print length of the book, and that's enough of a hint.
I like to let people know when my book is a short story. I include that information in the last line of my book descriptions. Something ...

You definitely want to avoid the kind of clash you're describing.
Intuitively, the section is composed of smaller subsections, which expand on particular areas. So a clash feels like you're saying "And now, within the topic of (Topic X), let's talk about (Topic X)." Even if there's some kind of sense to it, it's confusing and should be avoided.
The key to ...

The short answer to your general question is "no." If the subsection is titled the same as the section, then either one of them is named incorrectly or else your outline is incorrect. An outline is supposed to be like this:
Title: Great Cities of the World
I. American Cities
A. Large Cities
1. New York, NY
2. Chicago, IL
B. Historical Cities
...